What is istihadah (non-menstrual vaginal bleeding)? And what is the difference between hayd (menstruation) and istihadah?

Istihada (irregular vaginal bleeding) is blood that flows outside the usual menstrual period due to an illness or a vein, whereas menstruation (hayd) is the natural blood that a woman accustomed to monthly. Menstruation is distinguished from istihada by its dark color, unpleasant odor, and accompanying pain. Menstruation necessitates refraining from prayer, fasting, and sexual intercourse. It also prohibits entering the mosque, circumambulating the Kaaba (Tawaf), and touching the Mus'haf (Quran). A ghusl (ritual bath) is required afterward, based on Allah's saying: (And when they have purified themselves, then come to them from where Allah has ordained for you) and the Prophet's (peace be upon him) saying: "When your menstruation begins, stop praying, and when it ends, perform ghusl and pray." As for istihada, these rulings do not apply to it. A woman experiencing istihada is considered ritually pure, and she must perform ablution (wudu) for each prayer after its time has begun.